This invention relates generally to fuel system heaters and more particularly to a fuel delivery system having heater elements for heating fuel adjacent to the discharge opening of a fuel tank.
During cold weather it is often necessary to heat liquid fuels prior to introducing the fuel into a combustion device. Certain fuels and particularly diesel fuel oils tend to become more viscous at low temperatures during the winter months. As temperature decreases, typical diesel fuels tend to form wax or wax-like deposits which build up on the inner sides of the fuel tank and also collect on the interior walls of conduits connected to the tanks. If this wax builds up severely, flow to the combustion device is inhibited and often flow out of the tank is restricted or completely stopped by clogging of the fuel lines or tank outlet. In addition to wax accumulations within the tank, wax build-up is often encountered at the fuel discharge fitting where the fuel must make a sharp change in direction. A need therefore arises to provide heat inputs to the fuel system to provide a clear path of transmission of fuel from the storage tank to the associated combustion device.
One solution to inhibiting the formation of wax deposits in a fuel oil storage tank is to provide heating coils within the tank which circulate a hot liquid such as hot water originating from the cooling system of a diesel engine. This approach has the disadvantage that heating occurs only after the engine coolant has reached operating temperature and thus does not provide fuel heating when it is most critically needed, i.e., during start-up. Furthermore, this approach does not satisfactorily address heating requirements at the discharge fitting.
Another means of heating fuel is to provide a resistance heater element immersed into the fuel storage tank for warming the entire tank contents to prevent the formation of wax deposits. During extremely cold weather, however, waxing can still take place near the discharge of the tank and in the discharge fitting, thus clogging the discharge line. More importantly, this approach is extremely inefficient in terms of power input requirements.
The present invention eliminates the necessity for heating the entire fuel tank contents by providing a heater element adjacent or within the tank discharge fitting which ensures that a clear fuel flow path is provided out of the tank. The present invention utilizes a heating element such as a resistance heater positioned centrally within a hollow fuel discharge fitting. The heater according to the present invention can be energized prior to starting the engine to preheat the fuel delivery system or can be continuously energized.
Heat generated by the heater element of this invention is transferred directly to the fuel in the tank by means of convection in accordance with a first embodiment of the invention, or by a passive heat transfer element in thermal contact with the heater in accordance with alternate embodiments of the invention. The passive heat transfer elements extends through the tank discharge opening and into the tank to provide heat inputs at selected points within the tank.
Various types of passive heat transfer elements may be used with an active element in accordance with this invention. When a heat pipe is used as a passive conduction element, heat is transferred to the opposite end of the heat pipe by means of evaporation and condensation of the working fluid circulating within the heat pipe. Alternately, a solid metal rod can be used as a heat conducting passive element. In this way, heat is transferred by the passive element from the resistance heating element to the fuel in and near the discharge opening of the tank thereby providing a free flow passage for fuel from the tank through the interconnecting conduit and to the engine or an intermediate fuel processing device.
The fuel system heaters according to the present invention are generally positioned within the fuel outlet fitting in the lower side wall of the fuel tank at its bottom. Alternatively, a fuel tank with a top discharge fitting and a drawtube extending into the tank to a position near the bottom may be fitted with a heater in accordance with the present invention. In either application, a resistance heating element may be positioned within the fitting and a passive heat transfer element may be used having one end thermally coupled to the resistance heating element and extending down into the drawtube such that the fuel at the bottom of the drawtube is warmed to reduce wax build-up. To ensure that significant heat is transferred to the opposite end of the passive heat transfer element, an insulating sleeve may be provided around the element for a substantial portion of its length extending into the fuel tank thus precisely delivering heat to selected areas.
Devices according to this invention allow the free flow of fuel from the tank without requiring heating of the entire tank contents, thus providing efficient operation while ensuring that free flow of fuel is maintained. This approach minimizes the energy input requirements by focusing applied heat to the area most likely to cause flow problems.
Further objects, features, and advantages of the present invention will become apparent when taken in light of the attached drawings and following detailed description and appended claims.